Continuous process for conducting liquid phase chemical reactions

ABSTRACT

THIS DISCLOSURE DESCRIBES A PROCESS AND APPARATUS FOR CONTINUOUSLY CARRYING OUT A REACTION OF THE TYPE IN WHICH A GASEOUS PHASE IS DISPERSED THROUGHOUT A LIQUID PHASE TO MAINTAIN A PARTICULATE SOLID SUSPENDED IN THE LIQUID PHASE. THE REACTION IS CARRIED OUT IN AN ELONGATED REACTION VESSEL WHILE CONTINUOUSLY INTRODUCING LIQUID PHASE, AND CONTINUOUSLY WITHDRAWING LIQUID PHASE CONTAINING SOLID PHASE AND DISSOLVED PRODUCTS. A PORTION OF THE LIQUID PHASE CONTAINING THE DISSOLVED PRODUCTS IS CONTINUOUSLY COLLECTED AND A PORTION, TOGETHER WITH THE SOLID PHASE IS RETURNED TO THE REACTION MIXTURE. THE REACTION APPARATUS IS DESIGNED SO THAT UNDER THE CONDITIONS OF THE REACTION THERE IS A CONTINUOUS FLOW OF THE LIQUID PHASE THROUGHOUT THE APPARATUS WITHOUT PUMPING.

Dec. 25, 1973 G, GOBRON ETAL CONTINUOUS PROCESS FOR CONDUCTINC LIQUIDPHASE CHEMICAL REACTIONS Original Filed March 9, 1967 United StatesPatent O Im. c1. ook 31/18 U.S. Cl. 260-635 C 4 Claims ABSTRACT OF THEDISCLOSURE This disclosure describes a process and apparatus forcontinuously carrying out a reaction of the type in which a gaseousphase is dispersed throughout a liquid phase to maintain a particulatesolid suspended in the liquid phase. The reaction is carried out in anelongated reaction vessel while continuously introducing liquid phase,and continuously withdrawing liquid phase containing solid phase anddissolved products. A portion of the liquid phase containing thedissolved products is continuously collected and a portion, togetherwith the solid phase is returned to the reaction mixture. The reactionapparatus is designed so that under the conditions of the reaction thereis a continuous ow of the liquid phase throughout the apparatus withoutpumping.

This application is a division of copending patent application Ser. No.621,881, iiled Mar. 9, 1967, now U.S. Pat. 3,546,296.

FIELD OF INVENTION This invention is concerned with chemical reactionscarried out in the liquid phase in the presence of a solid phase whichis in particulate form and is held suspended by the force of thethroughput of the gaseous phase. The three phases together comprise thereaction mixture. The separate phases may be reactants or they may beinert. Thus the liquid phase may be a liquid reactant or it may be aninert solvent in Which one or more of the reactants is dissolved. Theproducts are soluble in the liquid phase. The solid phase may be areactant, a catalyst or simply an inert solid which aids in themechanical movement of the reaction mixture. The gas phase may be inert.It may also be a reactant or it may be the vapors of the liquid phase.The process is a continuous process in which the reaction mixture is incontinuous ow without the aid of auxiliary motive power such as pumps.The continuous ow is maintained by a combination of apparatus design andreaction conditions.

SUMMARY OF INVENTION In accordance with this invention, chemicalreactions, for example liquid phase hydrogenations are carried out in ansubstantially vertical elongated reaction vessel containing, in thebottom portion, the reaction mixture, comprising a liquid, gaseous, andsuspended solid phase. There is a void space above the surface of thereaction mixture, and the ratio of the volume of the void space to thevolume of the reaction mixture is from about 0.3 :l to about 1.5 z 1.Intermediate the bottom of the reaction vessel and the surface of thereaction mixture is a take-olf line including a decanter in which thesolid phase tends to settle. The de'- canter is located at leasttwo-thirds of the vertical distance from the bottom of the reactionmixture to the top surface of the mixture.

Means are provided for withdrawing a portion of the reaction mixturecontaining dissolved product from the 3,781,373 Patented Dec. 25, 1973ICC decanter. For example, a pipe located in the upper section of thedecanter will serve for the withdrawal of liquid phase substantiallyuncontaminated with the solid phase which settles to the lower sectionof the decanter.

The sludge in the lower section of the decanter, containing a relativelyhigh concentration of solid phase admixed with liquid phase, iswithdrawn through exit means, for example a pipe one end of which isaflixed to the lower section of the decanter. The other end is connectedto the lower portion of the reaction vessel so that the sludge can bereturned to the reaction mixture. The connection descends from thedecanter to the lower section of the reaction vessel. There is thusformed a closed circulatory system which, if the descending connectiondirectly connects the decander to the bottom of the reaction vessel, issubstantially in the form of a right triangle. It is not essential thatthe descending pipe be directly connected. It may be coupled to thedecanter through a substantially vertical connecting pipe descendingfrom the lower section of the decanter.

The liquid phase and the gaseous phase are introduced into the reactionmixture at the lower section of the reaction vessel. The gaseous phaseis Withdrawn from the top section of the void space in the reactionvessel.

As aforesaid, the gaseous phase may be a reactant, it may be inert, orit may be the vapors of the liquid phase. If the gaseous phase comprisesvapors of the liquid phase, they are preferably produced by distillationof the liquid phase fed to the lower section of the reaction vessel. Ifthe gaseous phase is a reactant it is preferably utilized in relativelylarge excess so that it is not all consumed in passing through theliquid phase. Consumption of the gaseous phase could cause the solidphase to settle to the bottom of the reaction vessel. If the gaseousphase is inert, or if it is the vapors of the liquid, it is onlynecessary to introduce or to produce in the bottom portion of thereaction vessel suflicient gaseous phase at a rate such as to keep thesolid phase suspended. The gaseous phase is withdrawn through the top ofthe reaction vessel.

It has been discovered that if the reaction is carried out underconditions such that the ratio of the specific weight of the mixture inthe descending pipe to the specic weight of the reaction mixture in thereaction vessel is at least l:0.8, and the ratio of the specic weight ofthe solid phase to the specific weight of the liquid in the decanter isat least 1.05 :1, there Will be continuous flow of liquid phase andsolid phase through the reaction apparatus.

In carrying out the reaction, the liquid is withdrawn from the decanterand the liquid and gas introduced into the reaction mixture at such arate that the volume of the reaction mixture remains substantiallyconstant.

The process of this invention is applicable to a wide variety ofreactions. Generally speaking, it is applicable to any and all liquidphase reactions in which a solid phase is dispersed throughout a liquidmedium and can be maintained suspended therein by a stream of gas orvapor passing through the liquid medium, whether or not the gas or vaporis a reactant.

There may be mentioned, for example, all reactions of the type in whichan ion exchanger, particularly an ion exchange resin, is used at acatalyst. Reactions of this kind include, for instance: aldolcondensations of aldehydes and/or ketones using anion exchange resins ascatalysts, or crotonization of aldehydes and/or ketones using cationexchange resins as catalysts, production of alkoxy compounds, such as al3-alkoxy carbonyl compound, for example, -methoxy propionaldehyde, froman alcohol, for example, meth-anol, and an ,-olefinic aliphatic carbonylcompound, for example, acrolein using anion exchange resins ascatalysts, and production of acetals from an aldehyde and an alcoholusing ion exchange resins as catalysts.

Other reactions include, for example, neutralization of hydrogen orhydroxyl ions in solutions utilizing anionic or cationic resins.Hydrogenation and dehydrogenation reactions carried out in the liquidphase in the presence of a dispersed solid catalyst, the liquid beingtraversed, respectively, by excess hydrogen or by vapors of the liquiditself may be carried out in accordance with this invention. A heatingdevice separate from the main reaction apparatus may be provided togenerate vapors of the liquid.

Generally speaking, the reaction conditions with respect to temperature,pressure and the like under which the above mentioned reactions arecarried out are similar to the conventional conditions usually employed.

The invention will now be described in detail as applied to liquid phasehydrogenations. The description is intended only as illustrative of theinvention, which as indicated above, is not limited to suchhydrogenations.

In accordance with this invention, liquid phase hydrogenations arecarried out in a substantially vertical, elongated reaction vessel in aliquid reaction meduim into the lower portion of rwhich the compound orcompounds to be hydrogenated are continuously introduced together with alarge volume of hydrogen and a solvent for both the reactant and theproducts. At the upper portion of the reaction medium suicient solutioncontaining dissolved reaction product is withdrawn so as to maintain thevolume of the reaction bath substantially constant. 'I'he reactionmedium contains dispersed hydrogenation catalyst, a portion of which iswithdrawn with the reaction product. Provision is made for returning thecatalyst, recovered solvent and hydrogen to the reaction bath.

'Ihe hydrogenation reactions in accordance with the process of thisinvention are carried out in a substantially vertical reaction vessel,which is extremely high compared with its other dimensions and which isonly partially filled with the reaction medium so that there is asubstantial amount of free space above the surface of the reactionmedium. The hydrogenation catalyst is maintained in suspension in thereaction bath. Hydrogen, reactant, and solvent, if necessary, arecontinuously fed into the lower portion of the bath and there iscontinuously withdrawn from the upper portion of the bath, a sufficientquantity of the bath to compensate for the quantities of materialsintroduced at the bottom of the bath. The rates of introduction andwithdrawal are kept at a level such that the volume of the reaction bathremains substantially constant. The hydrogenated product or products areseparated and the reaction solvent and catalyst are returned to thereaction bath.

In carrying out the process of the invention the preferred reactionvessel is an elongated cylindrical tube, although other congurations mayalso be used. The height to diameter ratio of the reaction bath in thevessel may vary from about 5:1 to about 65:1. Typically, the height ofthe bath may vary from 2 to 10 meters. With a Z-meter bath the diameteris normally from 0.03 to 0.10 meters, and with a meter bath the diameteris normally from 0.75 to 2 meters. Non-cylindrical baths are similarlydimensioned. The reaction bath is maintained in a substantially verticalposition.

The hydrogenation is eiected in a reaction bath containing from about20% to about 90% solvent based on the total weight of the components ofthe bath. Ihe solvent should be chemically inert under the reactionconditions. It should also dissolve both reactants'and products and itsboiling point under the reaction conditions should be sutciently abovethe reaction temperature so that solvent losses during the reaction arekept at a minimum. In the reaction bath the reactants are generallyconcentrated 1n the lower portion of the reaction zone, the productsconcentrate in the upper zone and in the middle zone the composition isintermediate these extremes.

Any of a wide variety of solvents or mixtures of solvents may beemployed. The selection of the particular solvent or solvent mixturedepends principally`on the solubility of the reactants and products, thereaction temperature and the boiling point of the solvent at theselected reaction pressure rwhich may be atmosperic, or above or belowatmospheric. 'Iypically useful solvents include, for example, mono orpolyhydric alcohols such as ethanol, nbutanol, 2ethyl-butanol, andxylitol; esters such as nbutyl acetate, 2ethyl-hexy1 acetate andZethyl-hexyl 2- ethyl hexanoate, hydrocarbons such as xylene andcyclododecane, ethers such as di-n-butyl ether and polyalkylene glycolethers, phenolic compounds such as phenol or toluol, and amines such ascyclohexylamine. It is often advantageous to employ the reaction productas the solvent. For example cyclohexylamine can be used as the solventfor the reduction of nitro cyclohexane to cyclohexylamine.

As aforesaid, there is a large empty volume in the reaction vessel abovethe reaction bath. The reason for this is that the strong gaseous streamwhich passes through the reaction bath entrains a part of the liquid inthe bath in the form of a mist which must travel for a considerabledistance in the void volume before resolving itself into fine dropswhich fall back into the reaction bath. In those cases where water isproduced as a by-product of the hydrogenation the water may be carriedon as an overhead with the solvent either by physical entrainment or asan azeotrope. It is advantageous in such cases to select a solvent whichis immiscible or only partially miscible with water so that aftercondensation of the vapors the water may be removed by simpledecantation and the solvent returned to the reaction bath.

The bath contains a finely divided hydrogenation catalyst dispersedtherethrough. The catalyst is of conventional kind. According to thecompound to be hydrogenated, there may be used, for example, nickeldeposited on a carrier, copper deposited on a carrier, etc. It is keptin suspension principally by the strong flow of hydrogen.

The hydrogenation temperature is chosen in conventional ranges accordingto the compound to be hydro genated. For example the temperature may befrom 50 C. to 150 C. Preferably it will be 20-30" C. lower than theboiling temperature of the solvent under the operating pressure.

Desirably the hydrogen is fed to the lowest part of the reaction zoneand the compound to be hydrogenated is introduced just above thehydrogen feed point. Withdrawal of liquid bath containing the reactionproduct or products is preferably eiected from the uppermost part of thebath, just below the upper level reached by the liquid bath during thehydrogenation operation. By suitably controlling the feed of compound tobe hydrogenated it is thus possible to obtain a raw reaction producthaving the lowest possible content of non-hydrogenated startingmaterial. For example the maximum feed rate of compound to behydrogenated is advantageously so chosen that the raw reaction productwithdrawn from the upper part of the bath contains no more than 200p.p.m. of non-hydrogenated starting material.

Preferably the amount of hydrogen utilized is such that the volume ofexcess hydrogen passing through the bath is from 3 to 6 times as largeas the volume of hydrogen consumed by the reaction during the same time.It is however possible to operate using a far lower amount of hydrogen,but to the detriment of the rate of production per unit of volume of thebath, or, on the contrary, a far higher amount thereof. In actualpractice it is advisable to provide such a cross-section of the reactorthat the rate of excess hydrogen passing therethrough is from 4 to 10cubic meters per hour per square decimeter of horizontal cross-sectionof the bath.

Preferably the liquid continuously withdrawn from the upper part of thebath is introduced into a decanting device in which the catalystseparates, in the form of a sludge, from the reaction products. Thecatalyst-liquid mixture deposited in the bottom part of the decantingdevice is sent back to the reaction zone while the clear,

supernatant liquid free from catalyst is withdrawn from the decanter andtreated in accordance with conventional techniques for separation of thecomponents thereof and recovery of the solvent which is re-used and ofthe desired hydrogenation product or products.

The following description with reference to the annexed drawing, whichis only illustrative and not limitative, will show a preferred manner ofcarrying out the invention.

The drawing is a schematic representation of an apparatus suitable forcarrying out the present process.

In the drawing the reaction vessel is a vertical, cylindrical tube 1iitted at its lower part with a heating device 2, for example a coilthrough which steam may be passed. The reactor contains the reactionbath the upper level of which, during the operation, is stabilized at 3as shown in the drawing. The bath is fed at its bottom part withhydrogen which is introduced through a pipe 4 by means of a pump 5 andis dispersed throughout the bath by means of a conventionalgas-dispersing device 6, for example a perforated plate, a porous plate,a perforated tube or the like. The bath is also fed, just above thehydrogen feed level, with the compound to be hydrogenated and thesolvent if a solvent is employed. The compound to be hydrogenated is fedthrough a pipe 7 either in pure conditionpossibly in molten state if itis a solid at room temperature-or dispersed throughout the solvent ifany. The solvent may be introduced, wholly or in part, apart from thecompound to be hydrogenated, through a pipe 8. Introduction of solvent,if a solvent is employed, is necessary to compensate for the withdrawalthereof from the upper part of the bath together with the reactionproducts.

The reaction mixture is continuously withdrawn from the reactor by apipe 9 and sent to a decanter 10 from which a catalyst-liquid mixturedeposited therein is withdrawn and sent back to the lower portion of thereaction bath by a pipe 11, While there is withdrawn by a pipe 12 therequired amount of clear, supernatant liquid to maintain the volume ofthe bath constant. The clear liquid withdrawn is then treated byconventional techniques to recover therefrom the solvent which is sentback to the bath, and the desired product or products which is or arecollected.

From the top of the reactor, by a pipe 13, issues the excess hydrogenladen with entrained solvent and reaction water, if any. 'This efuentmixture passes through a condenser 14 in which the entrained vapors areliquefied. In a separator 15 the residual gases separate from thecondensed liquid and are taken by a pipe 16 through which they are sentback into pipe 4 via pump S after receiving from a pipe 17 a suitableamount of fresh hydrogen to maintain the constancy of the gaseousstream. By a pipe 18 a controlled volume of gas is continuouslydiscarded from the gas circuit to maintain the purity of the hydrogen insaid circuit.

The solvent condensed in 14 and separated from the hydrogen in 15 issent back to the bath, wholly or partly (in the latter case the excesssolvent is withdrawn by a pipe 21 to be re-used later on), by pipes 19,20 and 11, to maintain constant the content of compound to behydrogenated in the lower portion of the reactor. In the case where thehydrogenation causes formation of reaction water, this water isseparated either by decantation in a decanter 22 from which the lower,water layer is withdrawn by a pipe 23, if the Water is immiscible withthe solvent and forms a layer distinct from the lsolvent layer, or, ifthis is not true, by distillation of the watercontaining, excess solventwithdrawn by pipe 21.

EXAMPLE 1 This example illustrates the production of tolylene diamine byhydrogenation of dinitro toluene (a commercial mixture of 80% by weightof the 2,4-isomer and 20% by weight of the 2,-6isomer).

In the apparatus employed, reactor 1 is 2.8 meters high and has an innerdiameter of 54 millimeters. Pipe 9 is situated 1.4 meters above thebottom of the reactor. The volume of decanter 10 is 2 liters.

Initially, reactor 1 is iilled with 4.2 kg. of a bath comprising, byWeight, 75% of 2-ethyl butanol and 25% of tolylene diamine. With thisamount of bath, the upper level of the bath during the hydrogenationoperation is stabilized just above pipe 9, at a height of 1.85 meters asshown in the drawing, and decanter 10 is full. To the bath is added 280g. of a nickel catalyst on a carrier.

There is fed to the bottom part of the reactor 2 m.3/hr. of hydrogen.The purity of the hydrogen in the gas circuit is kept at 95% by volumeby suitable control of the gas discarding through pipe 18.

The temperature of the reaction bath is adjusted to and maintained at120 C. and there is fed by pipe 7, 3785 g./hr. of a 15% (by weight)solution of dinitro toluene in 2-ethyl butanol.

The excess hydrogen issuing by pipe 13 entrains 2-ethyl butanol andWater which are condensed in condenser 14 and separated by decantationin decanter 22. The water is removed by pipe 23 and a part of the2-ethyl butanol is removed by pipe 21 for maintenance of an amineconcentration in the upper portion of the reaction bath of about 25 byweight.

The amount of liquid bath withdrawn per hour by pipe 9 is 2.7 liters.The amine produced is withdrawn by pipe 12 in the form of a 25% (byweight) solution in 2-ethyl butanol at a rate of 1.6 liters per hour ofthis solution, so as to maintain constant the level of the bath in thereactor.

The molar amine yield amounts to 98.7%. In the liquid withdrawn by pipe12 the dinitro toluene concentration is 30 p.p.m., the toluidineconcentration is 200 p.p.m. and the water concentration is 0.6% byweight.

In this example, the ratio of the specic weight of the mixture in pipe11 to the specific weight of the mixture in reactor 1 is about 2:1. Theratio of the specific Weight of the solid catalyst to the specificweight of the liquid in decanter 10 is about 4:1.

EXAMPLE 2 The example illustrates the production of xylitol byhydrogenation of xylose.

The apparatus is identical with that of Example 1 but is operated underpressure.

At starting, the reactor is iilled with a bath comprising, by weight, of80 vol. percent ethyl alcohol and 15% of xylitol. There is added to thisbath 280 g. of a nickel-on-carrier catalyst. The hydrogenation reactionis carried out under pressure of 5 kg./crn.2 eifective and at a bathtemperature of 100 C. Under these conditions the height of the reactionmixture is 1.7 meters.

There is fed to the bottom part of the reaction vessel 1 m.3/hr. ofhydrogen. The purity of the hydrogen in the gas circuit is kept at byvolume as disclosed in Example l. There is also fed to the lower part ofthe reactor 1120 g./hr. of a 15% (by weight) solution of xylose in 80vol. percent ethyl alcohol.

The Whole amount of aqueous ethyl alcohol condensed in condenser 14 issent back to the reactor and the xylitol solution is Withdrawn by pipe12 so as to maintain constant the level of the bath in the reactor.

The zylitol yield amounts to 99.8%.

In this example, the ratio of the specific weight of the mixture in pipe11 to the specific weight of the mixture in reactor 1 is about 1.3: 1.The ratio of the specific weight of the solid catalyst to the specificweight of the liquid in decanter 10 is about 5:1.

What is claimed is:

1. A continuous process for carrying out a liquid phase hydrogenation ofsugars to produce polyols wherein a hydrogen gas phase is dispersedthroughout a liquid phase containing said sugars to suspend aparticulate solid hydrogenation catalyst, which is a copper catalyst ora nickel catalyst, in which liquid phase said sugars dissolve to form areaction mixture, the process being carried out at or above atmosphericpressure in a closed reaction system in which the reaction mixture is incontinuo-us flow, which process comprises continuously forming saidreaction mixture while maintaining the same at a temperature of fromabout 50 C. to 150 C. in the lower portion of an elongated,substantially vertical reaction zone having a void space in the upperportion thereof, the ratio of the volume of void space to the volume ofthe reaction mixture in the lower portion of the reaction zone beingabout 0.3:1 to about 1.5 :l and the reaction mixture filling said lowerportion; continuously withdrawing a mixture containing at least a partof the liquid phase which contains reaction product together with atleast a part of the suspended solid catalyst from a point in the lowerportion, which point is at least two-thirds of the vertical distancefrom the bottom to the top of said lower portion of the reaction zone,the specific weight ratio of the solid catalyst to the liquid phase inthe withdrawn mixture being at least 1.05:1; separating and collecting asucient quantity of the liquid phase thus withdrawn at a rate so as tomaintain the volume of the reaction mixture substantially constant;returning to the reaction mixture the quantity of the liquid phaseremaining after separation together with the withdrawn gas phase fromthe top of the reaction zione, the specific weight ratio of saidreturned phase to the reaction mixture being at least 1:0.8.

2. A process in accordance with claim 1 in which the volume of hydrogenpassing through the reaction mixture per unit time is from 3 to 6 timesthe volume of hydrogen consumed by the reaction mixture during the sametime.

3. A procs in accordance with claim 1 in which the rate of excesshydrogen passing through the reaction is from about 4 to about 10 cubicmeters per hour per square decimeter of horizontal cross section of thereaction mixture.

4. A process in accordance with claim 1 in which water is a by-productof the hydrogenation reaction and is entrained with vapors of the liquidphase and with excess hydrogen and separated therefrom followingcondensation.

References Cited UNITED STATES PATENTS 3,478,103 ll/l96-9 Hann 260-635 C3,471,580 10/1969 Hellwig et al. 260-635 C 2,989,569 6/1961 Apel 260-635C 3,180,898 4/1965 Eisenlohr et al. 260-638 B HOWARD T. MARS, PrimaryExaminer J. E. EVANS, Assistant Examiner U.S. Cl. X.R.

260-563 C, 530, 602, 631 H, 638 A, 690

